Method for treating sulfides in waste streams

ABSTRACT

A method for treating sulfide in an aqueous fluid comprises contacting the fluid with an oxidizer in the presence of a sulfur dye or sulfurized vat dye. In one embodiment, the method comprises treating sulfide contaminated water by contacting the contaminated water with air in the presence of a sulfur dye or a sulfurized vat dye. The method is useful for remediating industrial, agricultural, and municipal waste water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is filed under the provisions of 35 U.S.C. § 120 and isa continuation of U.S. patent application Ser. No. 16/165,010 filed onOct. 19, 2018, now U.S. Pat. No. 10,315,940 issued on Jun. 11, 2019,which is a divisional of U.S. patent application Ser. No. 14/854,403filed Sep. 15, 2015 in the name of William Moseley Archer III, now U.S.Pat. No. 10,112,853 issued on Oct. 30, 2018, which are herebyincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to the treatment of aqueous solutionscomprising sulfides. More particularly, the present invention is aprocess for the treatment of sulfides in an aqueous solution wherein theaqueous solution comprising the sulfides is contacted with a sulfur dye.The present invention is useful for the remediation of sulfides found innatural and industrial aqueous waste streams, or waste water. Moreparticularly, the waste water comprising sulfides can result fromindustrial operations such as animal waste processing, mining, orerefining, oil drilling, petroleum refining, natural gas processing, andhydraulic fracturing.

BACKGROUND

Sulfide is an unwanted component of many waste streams. It can occurnaturally or as the result of industrial processes. It also is generatedby the absorption of hydrogen sulfide in an aqueous liquid as is commonin scrubber systems, particularly alkaline scrubbers. If the scrubberliquid is alkaline a portion of the hydrogen sulfide will be convertedto dissolved bisulfide (HS⁻) and sulfide (S⁻²). The proportion of thesespecies depends on the pH of the liquid. The term sulfide used in thisinvention includes all forms of inorganic sulfide including hydrogensulfide, bisulfide ions, sulfide ions and polysulfide ions. If alkalinesulfide-bearing solutions are neutralized or acidified, soluble sulfidesare converted to hydrogen sulfide, potentially off-gassing from theliquid. Hydrogen sulfide gas is malodorous and toxic. Liquids thatcontain sufficiently high levels of sulfide are classified by US EPAregulations as reactive hazardous wastes because of their potential togenerate hydrogen sulfide when acidified. It is often desirable toremove or destroy sulfides present in aqueous fluids. One method ofeliminating sulfides is to oxidize them to a new compound that is notmalodorous or toxic.

Oxidation of sulfides in aqueous liquids can be accomplished chemicallywith oxidizing agents such as hydrogen peroxide, chlorine dioxide,hypochlorite salts, methylmorpholine-N-oxide, or nitrate/nitrites. Thesemethods are effective but have drawbacks which can include high chemicalcosts, handling of hazardous chemicals and formation of unwantedby-products. Oxidation can be accomplished biologically, but this isusually expensive and can produce odors in the treatment units. A thirdmethod is oxidation with molecular oxygen in the presence of a catalyst.Sulfides may also be treated by other methods such as absorption orsequestering.

The most common catalyst for sulfide oxidation is a chelated metalcatalyst, most particularly iron chelated by an aminopolycarboxylicacid. The normal product of oxidation with this catalyst in aqueousfluids is elemental sulfur which precipitates. The catalyst is typicallyregenerated with molecular oxygen, normally atmospheric air which canalso degrade the catalyst. This method for oxidizing sulfides is notwithout drawbacks. It requires removal of solid elemental sulfur andreplenishment of catalyst.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an inexpensive alternative to thetraditional treatment of sulfides by expensive chemicals or by oxygencatalyzed by chelated metal which creates a sulfur precipitate. It hasbeen discovered that sulfur dyes and sulfurized vat dyes will oxidizesulfides dissolved in aqueous fluids when the fluid is contacted withoxygen, typically atmospheric air. The present invention uses smallamounts of inexpensive dye as a means for oxidation of sulfides in thepresence of oxygen or other oxidizers. Sulfur dyes and sulfurized vatdyes are stable under the highly alkaline conditions often associatedwith absorption or scrubbing of hydrogen sulfide from gaseous streams.Sulfide oxidation under alkaline conditions in the presence of sulfurdye is very simple and predominantly produces a non-toxic solubleby-product, thiosulfate. In many applications, the soluble nature of thetreatment product will be an advantage.

In one embodiment, the present invention is a method for treatingsulfide in an aqueous fluid comprising contacting the fluid with anoxidizer in the presence of at least one sulfur dye or sulfurized vatdye.

In a further embodiment, the present invention is a method for treatingoilfield waste water. The method comprises contacting the oilfieldwastewater with an oxidizer in the presence of at least one sulfur dyeor sulfurized vat dye.

In a still further embodiment, the present invention is a method fortreating sulfide produced by hydrogen sulfide absorption in an alkalineaqueous liquid to form an adsorption liquid comprising dissolvedsulfides. The method comprises contacting the absorption liquid with atleast one sulfur dye or sulfurized vat dye and concurrently orsubsequently contacting the absorption liquid with an oxidizer toprovide a treated liquid.

DETAILED DESCRIPTION OF THE INVENTION

The method can be operated over a wide range of conditions, includingtemperature, sulfide concentration, dye concentration, and oxygen input.

The rate of sulfide treatment is dependent, at least to some extent, onall four of these parameters. While a higher temperature will generallyincrease the reaction rate, a higher temperature will also tend toreduce the solubility of oxygen in water. Solubility of oxygen in wateris increased by higher pressure. The optimum conditions for best economydepend greatly on the particular circumstances. Since the presentinvention has utility in a vast range of applications, the optimumconditions will vary widely also. The examples provided demonstrate therobust nature of this method over a wide range of conditions.

The process may be utilized in numerous waste water treatmentapplications. Addition of sulfur dye and introduction of oxygen tovirtually any sulfide bearing aqueous solution will reduce the sulfideconcentrations. Sulfide treatment systems can be set up to operatecontinuously or as batch processes. The method will have applications inoil field operations to reduce sulfide in waters associated with oil andgas production. In one embodiment, the sulfur dye is retained byfiltration, ultrafiltration, or other means of separation to allow thetreated water and soluble salts to be reused in the oilfield operation.The method of this invention may also be used in downhole treatment ofsulfide bearing waters in oilfields.

In a very simple application, small amounts of sulfur dye added to wastewater impoundments can provide very economical sulfide treatment whereoxygen input is accomplished by surface transfer of atmospheric oxygen.

In one embodiment, the method can be incorporated into the absorptionprocess for removing hydrogen sulfide from gaseous streams. Sulfur dyecan be added directly to an aqueous absorption liquid having a pHgreater than 7, where an oxidizer, typically comprising or containingoxygen or air, is added to the system. Preferably, the absorption liquidis sufficiently alkaline (having a pH greater than 9) to facilitate theabsorption of hydrogen sulfide. Molecular oxygen, typically atmosphericair, can be added at any convenient place in the absorption system. Atreatment unit may be operated at greater than atmospheric pressure tofacilitate the dissolving or contacting of the oxygen in the aqueousabsorption liquid. Under the alkaline conditions employed to absorbhydrogen sulfide into an aqueous liquid, it is believed that the primaryproducts of the treatment with the sulfur dye are thiosulfates. The formof the thiosulfates are typically sodium or potassium thiosulfatedepending on which alkali (such as: sodium hydroxide or potassiumhydroxide) is used in the absorption liquid. Optionally, filtration,ultrafiltration or other means of separation can be used to separate thesoluble products of the sulfide treatment from any insoluble sulfur dyethat is retained by the separator. Sulfur dye compounds separated inthis manner can be reused in the sulfide oxidation process.

The sulfur dyes and sulfurized vat dyes which may be used in accordancewith the process of the invention include those which are either 1)provided in the non-reduced (oxidized) form (where sulfur atoms attachedto the dye chromophore are predominantly connected to other chromophoreunits through disulfide or polysulfide linkages), 2) provided aspre-reduced (leuco) sulfur dyes (where sulfur atoms exist primarily asthiolate salts), or 3) provided as solubilized sulfur dyes where Buntesalt groups impart water solubility under non-reducing conditions.

Sulfurized vat dyes are chemically and structurally similar to sulfurdyes including having the disulfide/thiolate functionality. They aregiven the vat dye designation because they are typically dyed using avat dye process.

Sulfur dyes and sulfurized vat dyes can be dissolved by reducing agentssuch as sodium sulfide, sodium dithionite or sodium hydrosulfide underalkaline conditions. This reduction breaks the disulfide bonds producingvery polar thiolate groups (Dye-S⁻). This form of the dye is called aLeuco Sulfur Dye. The oxidation/reduction of the sulfur atoms attachedto the chromophore structure is reversible as follows:2 Dye-S⁻+oxidizer>Dye-S—S-Dye+reducing agent>2 Dye-S⁻

Sulfur dyes can also exist as a non-reduced, water soluble formcharacterized by thiosulfate groups attached to the chromophores(Dye-S—SO₃ ⁻). This form is called a Bunte Salt and is categorized as aSolubilized Sulfur Dye. Solubilized Sulfur Dyes can be prepared byoxidative reaction of a sulfur dye with sulfite. Solubilized Sulfur Dyeswill convert to one of the other dye forms when reacted with sulfides.Any of the three forms of sulfur dyes may be used in accordance withthis method.

During sulfur dye production and dyeing processes, sulfides can undergooxidation when leuco dyes are converted to the insoluble non-reduced(oxidized) form with air. However, this oxidation of sulfides has notbeen attributed to the presence of the dye. There is no evidence thatanyone has recognized that the addition of sulfur dyes or sulfurized vatdyes will act as a catalyst for the treatment of unwanted sulfides inwaste waters and other aqueous fluids. It has been discovered that thesedyes, even in very low molar concentrations, will treat sulfides inaqueous fluids.

It is believed that the mechanism of the sulfide treatment of thepresent invention is that the sulfur dye in the non-reduced (oxidized)form reacts with sulfide in solution to oxidize the sulfide to aharmless compound, such as sodium thiosulfate. In reacting the sulfurdye in the sulfide treatment process, the sulfur dye is converted to theleuco (reduced) form of the dye. When the thus produced leuco form ofthe dye is contacted with oxygen or another suitable oxidizer, the leucodye is restored to the non-reduced state ready to react with moresulfide. If the absorption liquid is contacted with a leuco form of thesulfur dye; it is required to simultaneously contact the absorptionliquid with an oxidizer such as air to provide the sulfide treatment.While the exact structures and molecular weights of most sulfur dyes arenot known, the molecular weight of an individual chromophore unit ofSulfur Black 1 is believed to be about 548 based on a common proposedstructure. This molecular weight is about 14 times the weight of asulfide ion. The method of this invention is demonstrated to be veryeffective at molar ratios of sulfur dye to sulfide that are less than 1mole-%. More preferably, the molar ratio of sulfur dye to sulfide iseffective at less than about 0.6 mole-%. This strongly supports that thedye used in this method acts as a catalyst to provide the sulfidetreatment.

Sulfur dyes and sulfurized vat dyes which may be utilized in accordancewith the method of the invention include but are not limited to thefollowing (“C.I.” stands for “Colour Index”):

C.I. Sulfur Yellow 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 16, 20and 23, C.I. Leuco Sulfur Yellow 2, 4, 7, 9, 12, 15, 17, 18, 21, 22 and23 and C.I. Solubilized Sulfur Yellow 2, 4, 5, 19, 20 and 23;

C.I. Sulfur Orange 1, 2, 3, 4, 5, 6, 7 and 8, C.I. Leuco Sulfur Orange1, 3, 5 and 9 and C.I. Solubilized Sulfur Orange 1, 3, 5, 6, 7 and 8;

C.I. Sulfur Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12 and 13, C.I. LeucoSulfur Red 1, 4, 5, 6, 11 and 14 and C.I. Solubilized Sulfur Red 3, 6,7, 11 and 13;

C.I. Sulfur Violet 1, 2, 3, 4 and 5, C.I. Leuco Sulfur Violet 1 and 3and C.I. Solubilized Sulfur Violet 1;

C.I. Sulfur Blue 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18 and 19, C.I. Leuco Sulfur Blue 1, 2, 3, 5, 7, 8, 9, 11, 13, 15and 20 and C.I. Solubilized Sulfur Blue 1, 2, 4, 5, 6, 7, 10, 11, 13,and 15;

C.I. Sulfur Green 1, 2, 3, 4, 5, 6, 7, 8:1, 9, 10, 11, 12, 13, 14, 15,16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 31, 32 and 33,C.I. Leuco Sulfur Green 1, 2, 3, 4, 7, 11, 16 30, 34, 35, 36, and 37 andC.I. Solubilized Sulfur Green 1, 2, 3, 6, 7, 9, 19, 26, and 27;

C.I. Sulfur Brown 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 14:1,15, 15:1, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,49, 50, 51, 52, 53, 53:1, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64,65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 76, 77, 78, 79, 84, 85, 87, 88,89, 90, 91, 93, and 94;

C.I. Leuco Sulfur Brown 1, 3, 4, 5, 8, 10, 11, 12, 14, 15, 21, 23, 26,31, 37, 43, 44, 81, 82, 86, 87, 90, 91, 92, 93, 94, 95 and 96 and C.I.Solubilized Sulfur Brown 1, 4, 5, 8, 10, 11, 12, 14, 15, 16, 21, 26, 28,31, 51, 52, 56, 60, 75, 80, and 83;

C.I. Sulfur Black 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16and 17;

C.I. Leuco Sulfur Black 1, 2, 6, 9, 10, 11, and 18;

C.I. Solubilized Sulfur Black 1, 2, 5, 7, and 11; and,

C.I. Vat Yellow 21, C.I. Vat Orange 21, C. I Vat Green 7, C.I. Vat Blue7, 42, 43, Vat Black 11.

A more complete listing of the sulfur dyes and sulfurized vat dyesmentioned hereinabove may be found in the Colour Index, 3rd. Ed., issuedby the Society of Dyers and Colourists (London, GB), as well as in thesupplementary volumes published thereto and in the Colour IndexInternational, 4^(th) Edition Online which are hereby incorporated byreference.

At least one sulfur dye or sulfurized vat dye listed hereinabove is usedto treat aqueous sulfides in the process of the instant invention. Morepreferably, at least one of C.I. Sulfur Black 1, C.I. Leuco Sulfur Black1 and C.I. Solubilized Sulfur Black 1 is utilized in accordance with theprocess to treat sulfides based on economics and availability.

Compounds other than those listed by Colour Index International mayexist or be synthesized which chemically qualify as sulfur dyes orsulfurized vat dyes and may be utilized in accordance with the method ofthis invention. Such compounds might not possess a sufficientlydesirable color or fastness to be offered as a dye, yet performacceptably in the method of this invention. The terms “sulfur dye” and“sulfurized vat dye” as used in this invention include compoundscomprised of monocyclic aromatic, heteroaromatic, or quinoid chromophoreunits; or polycyclic aromatic, heteroaromatic, or quinoid chromophorewherein said chromophore units are connected by disulfide or polysulfidelinkages when in the non-reduced form. Sulfur dyes and sulfurized vatdyes can be converted to the reduced (or leuco) form by reaction withreducing agents such sodium sulfide, sodium dithionite or sodiumhydrosulfide. This reaction cleaves the disulfide linkages of thenon-reduced (oxidized) dye to form thiolate functional groups (dye-S⁻).This conversion between disulfide and thiolate functionality isreversible.

A series of examples was developed and carried out to explore theconcept of the method for treating aqueous solutions containing sulfidesby contacting the aqueous solution containing the sulfide with a sulfurdye or sulfurized vat dye. It was discovered that the concentration ofsulfide in the aqueous sulfide solutions could be reduced by more than90 percent on the basis of the weight of the sulfide present in theaqueous sulfide solution. More preferably, the concentration of sulfidein the aqueous sulfide solutions could be reduced by more than 95percent on the basis of the weight of the sulfide present in the aqueoussulfide solution. Most preferably, the concentration of sulfide in theaqueous sulfide solutions could be reduced by more than 96, 97, 98, 99,or 99.5 percent on the basis of the weight of the sulfide present in theaqueous sulfide solution. The process of the present invention wasdemonstrated over a reaction temperature range of from about 1° C. toabout 100° C. More preferably, the process of the present invention canbe carried out over a reaction temperature of from about 4° C. to about80° C. Most preferably, the process of the present invention can becarried out over a reaction temperature of from about 20° C. to about50° C. The sulfur dye was dissolved in aqueous sulfide solutions insulfur dye concentrations ranging from about 10 to about 1200 mg/l.These dye concentrations are based on the concentration of commercialdye products which contain less than 100% active dye ingredient. Overthe entire range of aqueous sulfide solutions having a concentration ofsulfide from about 100 to about 5000 mg/l, it was found that theaddition of sulfur dye or sulfurized vat dye resulted in a greater than96 weight percent reduction of the sulfide in the aqueous sulfidesolutions within a treatment time ranging from about 30 minutes to about120 minutes. When using Sulfur Black 1 as the sulfur dye, the reductionof the sulfide concentration ranged from about 97 to about 99.6 weightpercent based on the initial amount of sulfide in the aqueous sulfidesolution to be treated, reducing the final concentration of sulfide fromas high as about 5000 mg/l to as low as less than about 1 mg/l sulfidein the treated effluent. Table 1 shows a summary of the results ofexperiments related to the reduction of sulfides in aqueous solutionsusing sulfur dyes and sulfurized vat dyes compared to a reference case(Zero) wherein no sulfur dye or sulfurized vat dye was added to theaqueous sulfide solution.

TABLE 1 Comparison of Sulfide Treatment with Sulfur Dyes and SulfurizedVat Dyes Treat- Dye Sulfide Sulfide ment Reduc- Ex. Conc. Temp InitialFinal Time tion No. Dye mg/l ° C. (mg/l) (mg/l) (Min) % Zero None 043-46 500 >490 120 <2 1 Sulfur Black 1 251 43-46 478 <1  50 99.6 2Sulfur Black 1 250 4-6 250 <5 120 >98 3 Sulfur Black 1 250 78-80 250 <1 30 >99.6 4 Sulfur Black 1 10 42-45 100 3  30 97 5 Sulfur Black 1 247.550 495 6 105 98.8 (reused) 6 Leuco Sulfur 1200 45-48 500 <20  60 >96Brown 37 7 Leuco Vat 1200 44-45 500 <2.5  60 >99.5 Blue 43 8 SulfurBlack 1 500 40-45 5000  20  75 99

EXAMPLES

The following examples are intended to demonstrate the wide range ofconditions under which sulfur dyes and sulfurized vat dyes are effectivein treating sulfide when an oxidizer (in these examples air) isintroduced into the aqueous fluid which contains the sulfide.

Example Zero+Control without Dye

A 1000 mg/l stock sulfide solution (as S⁻²) was made by dissolving 1.503grams of sodium sulfide nonahydrate in distilled water and diluting itto 250 milliliters. A 100 milliliter sample of 500 mg/l sulfide testsolution was made by diluting 50 milliliters of the stock solution to100 milliliters with distilled water. An aliquot was taken from thesulfide test solution for analysis under buffered pH and ionic strengthconditions using a sulfide specific ion electrode calibrated usingfreshly prepared sulfide standards. (This method of analysis was usedfor all sulfide analyses in the examples.) The test solution was stirredand heated to 45° C., at which time an air sparge through a diffuser wasinitiated. The stirred and aerated test solution was maintained at atemperature of 45+/−2° C. Samples were withdrawn for analysis every 30minutes for 2 hours. A decrease in sulfide concentration of less than 2%relative to the initial sulfide concentration of 500 mg/l was observedafter two hours, demonstrating that the sulfide concentration was notmarkedly affected by the test conditions.

Example 1—C. I Sulfur Black 1

While the initial test of Example Zero was underway, a 1% solution ofC.I. Sulfur Black 1 product was prepared by diluting 1 gram of C.I.Sulfur Black 1 to 100 milliliters with distilled water while stirringand heating to 80° C. A 1.8 milliliter portion of the 1% solution wasadded to the remaining 70 milliliters of test solution from Example Zeroto produce a calculated sulfide concentration of 478 mg/l and a SulfurBlack 1 product concentration of 251 mg/l. The test solution wasmaintained at the same test conditions of temperature, stirring and airsparging as the control in Example Zero. After 30 minutes of sparging,the sulfide concentration in the test sample of Example 1 had decreasedto less than 10 mg/l. After 50 minutes the sulfide concentration in thetest sample of Example 1 had dropped to less than 2 mg/l; a reduction ofapproximately 99.6% relative to the initial sulfide concentration of 478mg/l.

Example 2—C.I. Sulfur Black 1

A test solution containing 250 mg/l sulfide and 250 mg/l of C.I. SulfurBlack 1 product was made by diluting 25 milliliters of the 1000 mg/lsulfide stock solution prepared in Example Zero with 72.5 milliliters ofdistilled water. The test solution of Example 2 was cooled to 5° C., andthen 2.5 milliliters of the 1% Sulfur Black 1 solution prepared inExample 1 was added. The test solution of Example 2 was stirred andsparged with air as in Example 1, while maintaining the test solution ofExample 2 at a temperature in the range of 4-6° C. with an ice bath.After 120 minutes a sample of the test solution of Example 2 wascollected, and determined to have a sulfide concentration of less than 5mg/l. This resulted in a reduction of sulfide content by about 98%relative to the initial sulfide concentration of 250 mg/l.

Example 3—C.I. Sulfur Black 1

This test used similar test conditions to Example 2. A test solutioncontaining 250 mg/l sulfide and 250 mg/l of Sulfur Black 1 product washeated to 80° C. at which time air sparging was initiated. After 15minutes of sparging the sulfide concentration had decreased toapproximately 5 mg/l and after 30 minutes, the sulfide concentration haddecreased to less than 1 mg/l, a reduction of over 99.6% relative to theinitial sulfide concentration of 250 mg/l.

Example 4

This test was performed under similar conditions to Example 1 exceptthat the initial sulfide concentration was 100 mg/l and the sulfur dyeproduct concentration was 10 mg/l. After air sparging for 30 minutes ata temperature of 42-45° C., the sulfide concentration had decreased toless than 3 mg/l. This represents a reduction in the sulfideconcentration of about of 97% relative to the initial sulfideconcentration of 100 mg/l.

Example 5—C.I. Sulfur Black 1

This example demonstrates that the dye component can be reused. Aftertreating a test solution of 500 mg/l sulfide and 250 mg/l Sulfur Black 1by air sparging at 50° C. to a final sulfide concentration of less than1 mg/l, the used mixture was replenished with sulfide and re-treated. A1.75 milliliter portion of 5% sulfide was added to 175 milliliters ofused sulfur dye test mixture producing calculated concentrations of 495mg/l sulfide and 247.5 mg/l sulfur black product. This replenishedmixture was stirred and sparged at 50° C. for 105 minutes resulting in afinal sulfide concentration of approximately 6 mg/l, a 98.8% reductionin sulfide concentration relative to the initial sulfide concentrationof 495 mg/l.

Example 6—C.I. Leuco Sulfur Brown 37

This test was similar to previous tests except a sulfur dye productcontaining C.I. Leuco Sulfur Brown 37 was used to treat the sulfidesolution instead of C.I. Sulfur Black 1. A solution of C.I. Leuco SulfurBrown 37 dye was made by diluting 6 grams of DIRESUL Brown RDT-GS liq150, a liquid dyestuff solution of C.I. Leuco Sulfur Brown 37 dye(Available from Archroma U.S., Inc., Charlotte, N.C.) to 50 milliliterswith distilled water. A 500 mg/l sulfide test solution was prepared bydiluting 50 milliliters of 1000 mg/l stock sulfide solution to 99milliliters. This solution was heated to 45° C. and 1 milliliter of thediluted Brown dye was added to produce a solution containing 1200 mg/lof formulated dye product. The solution was stirred and sparged as inprevious examples. After 30 minutes the sulfide level had dropped byapproximately 90%. After 60 minutes the sulfide concentration was lessthan 20 mg/l, a greater than 96% reduction in sulfide concentrationrelative to the initial sulfide concentration of 500 mg/l.

Example 7—C.I. Leuco Vat Blue 43

This test was similar to previous tests except a dye product containingC.I. Leuco Vat Blue 43 was used to treat the sulfide solution. Asolution of C.I. Leuco Vat Blue 43 dye was made by diluting 12 grams ofDIRESUL Navy RDT-GF 1 liq dyestuff product (Available from ArchromaU.S., Inc., Charlotte, N.C.) to 100 milliliters with distilled water. A500 mg/l sulfide test solution was prepared by diluting 50 millilitersof 1000 mg/l stock sulfide solution to 99 milliliters. This solution washeated to 45° C. and 1 milliliter of diluted Navy dye was added toproduce a solution containing 1200 mg/l of formulated dye product. Thesolution was stirred and aerated as in previous examples. After 30minutes the sulfide level had dropped by more than 98% to less than 10mg/l. After 60 minutes the sulfide concentration was less than 2.5 mg/l,a greater than 99.5% reduction in sulfide concentration relative to theinitial sulfide concentration of 500 mg/l.

Example 8—C.I. Sulfur Black 1

A test sulfide solution was made by dissolving 3.745 grams of sodiumsulfide nonahydrate in distilled water and diluting to a total volume of99 milliliters. This solution was heated to 45° C. One milliliter of 5%C.I. Sulfur Black 1 solution was then added to produce a test solutionof 5000 mg/l sulfide and 500 mg/l Sulfur Black 1. The test solution wasstirred and sparged with air while maintaining the test solutiontemperature in the 40-45° C. range. After 75 minutes a sample wascollected and determined to have a sulfide concentration of slightlyless than 50 mg/l, a reduction of approximately 99% relative to theinitial sulfide concentration of 5000 mg/l.

I claim:
 1. A method for treating sulfides in a waste water impoundmentcomprising: introducing at least one sulfur dye or sulfurized vat dye tothe waste water impoundment; contacting the waste water with oxygen tooxidize the sulfides to soluble sulfur-containing salts, wherein atleast a portion of said oxygen is supplied by surface transfer ofatmospheric oxygen, thus providing a treated water having a reducedconcentration of sulfides relative to the waste water; and separatingthe soluble sulfur-containing salts from the at least one sulfur dye orsulfurized vat dye in the treated water.
 2. The method of claim 1,wherein said sulfides are selected from the group consisting of hydrogensulfide, bisulfide ions, sulfide ions, polysulfide ions and mixturesthereof.
 3. The method of claim 1, wherein said sulfur dye is selectedfrom the group consisting of Sulfur Black 1, Leuco Sulfur Black 1,Solubilized Sulfur Black 1 and mixtures thereof.
 4. The method of claim1, wherein the oxidation of the sulfides occurs under alkalineconditions.
 5. The method of claim 1, wherein the sulfur dye orsulfurized vat dye separated from the treated water is reused.
 6. Themethod of claim 5, wherein the separation can be effectuated usingfiltration or ultrafiltration.
 7. The method of claim 1, wherein thetreatment operates continuously or as batch processes.